AUTHOR=Hoshika Yasutomo , Paoletti Elena , Agathokleous Evgenios , Sugai Tetsuto , Koike Takayoshi TITLE=Developing Ozone Risk Assessment for Larch Species JOURNAL=Frontiers in Forests and Global Change VOLUME=3 YEAR=2020 URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2020.00045 DOI=10.3389/ffgc.2020.00045 ISSN=2624-893X ABSTRACT=

Ozone (O3) risk assessment for the protection of forests requires species-specific critical levels (CLs), based on either O3 concentrations (AOT40) or stomatal uptake (PODY) accumulation over the growing season. Larch (Larix sp.) is a genus with O3-susceptible species, widely distributed in the northern hemisphere and with global economic importance. We analyzed published and unpublished data of Japanese larch (Larix kaempferi) and its hybrid F1 (Larix gmelinii var. japonica × L. kaempferi) stomatal responses for developing a parameterization of stomatal conductance model and estimating PODY-based CLs with two Y thresholds, that is, 0 and 1 nmol m–2 s–1 projected leaf area (PLA). In parallel, we estimated AOT40-based CLs. The results show that the AOT40-based CLs for a 2% and 4% biomass loss in Japanese larch were 5.79 and 11.59 ppm h, that is, higher than those in hybrid larch F1 (2.18 and 4.36 ppm h AOT40), suggesting a higher O3 susceptibility of the hybrid. However, the use of PODY reconciled the species-specific differences, because the CLs were similar, that is, 9.40 and 12.00 mmol m–2 POD0 and 2.21 and 4.31 mmol m–2 POD1 in Japanese larch versus 10.44 and 12.38 mmol m–2 POD0 and 2.45 and 4.19 mmol m–2 POD1 in the hybrid, for 2% and 4% biomass loss, respectively. Overall, the CLs were lower than those in other forest species, which suggests a relatively high susceptibility of these larches. These results will inform environmental policy-makers and modelers about larch susceptibility to O3.